DE69208095T2 - Catalyst and process for oligomerizing olefins - Google Patents

Abstract

PCT No. PCT/EP92/02286 Sec. 371 Date Feb. 10, 1994 Sec. 102(e) Date Feb. 10, 1994 PCT Filed Oct. 2, 1992 PCT Pub. No. WO93/06926 PCT Pub. Date Apr. 15, 1993.A catalyst, which is active in the oligomerization of olefins is an X-ray-amorphous silica-alumina-nickel oxide gel having an SiO2/Al2O3 molar ratio of from 30/1 to 500/1, and NiO/SiO2 molar ratio of from 0.001/1 to 0.01/1, a superficial area of from 500 m2/g to 1.000 m2/g, and a porosity of from 0.3 ml/g to 0.6 ml/g, the means pore diameter being 1 nm (10 Angstrom), and devoid of pores having a diameter over 3 nm (30 Angstrom). The catalyst selectively dimerizes isobutene into alpha- and beta-isobutene and oligomerizes propylene into its relative dimers and trimers. A process is described for preparing the silica-alumina-nickel oxide gel.

Description

The present invention relates to an active silica/alumina/nickel oxide gel, the process for its preparation and its use in processes for dimerizing isobutene to α- and β-diisobutene and cligomerizing propylene to the respective dimers and trimers.

The usual processes used in the dimerization of isobutene are generally based on the use of an acid catalyst such as sulfuric acid, polyphosphoric acid (in liquid form or on an inorganic solid), heteropolyacids, i.e. polymolybdenum and silicotungstic acid, ion exchange resins of the polystyrenesulfonic acid or fluorosulfonic acid type, boron trifluoride complexes with alcohols, organic acids, esters, ethers, ketones, aluminum trichloride together with ethyl ether, hydrochloric acid or nitromethane, simple or complex salts, in particular nickel salts activated with an aluminum alkyl or an aluminum alkyl halide and metal oxides such as bismuth oxide, optionally together with a phosphorus oxide.

Catalysts that are capable of oligomerizing olefins such as polypropylene and butenes are in turn aluminosilicates and zeolites, which are optionally modified with salts or oxides of metals such as nickel, chromium and cobalt, as described, for example, in US-A-3 518 323 and UA-A-3 525 456, EP-A-132 172, EP-A-224 228, EP-A-133 052.

Finally, US-A-3 960 978, US-A-4 150 062 and EP-A-311 676 describe processes for producing gasoline by olefin oligomerization with zeolites of the ZMS-6 type.

Gasoline obtained in this way also contains a proportion of aromatic hydrocarbons, mainly benzene, which are undesirable due to their toxicity to humans and the environment.

Many of the conventional oligomerization catalysts have disadvantages due to the corrosive effect of the acids used, the requirement to dispose of the spent catalysts, their limited lifetime and/or the cost of their manufacture. A problem common to these conventional catalysts is their low selectivity towards the desired reaction products. For example, when used for the dimerization of isobutene, they lead to the formation of appreciable amounts of higher oligomers and isomers other than the particularly desirable ones, ie α- and β-diisobutene.

Finally, when an isobutene stream mixed with other C4 olefins undergoes dimerization, co-dimers are usually formed simultaneously.

This is believed to be due to the relatively high temperatures at which the usual catalysts develop their activity or the extremely high acidity of the catalysts themselves, which allows molecular rearrangements or other undesirable side reactions. EP-A-340 868 describes an amorphous and microporous silica/alumina gel which is active in isomerization, alkylation, dewaxing and dimerization processes of linear olefins.

According to the present invention, it has now been shown that the introduction of limited amounts of nickel oxide into a gel of the type indicated in the above-mentioned EP-A-340 868 makes it possible to obtain a catalyst with a uniform and controlled porosity, which is substantially free of isomerization ability and is able to dimerize isobutene to α- and β-diisobutene with surprisingly high selectivity. It is therefore possible to obtain high quality products which are suitable as chemical intermediates or for the production of high octane gasoline. It has further been shown that such a catalyst is effective for the oligomerization of propylene to dimers and trimers which are suitable as such or after etherification as high octane gasolines. In accordance with the above, a first aspect of the present invention relates to an X-ray amorphous silica/alumina/nickel oxide gel having a SiO₂/Al₂O₃ molar ratio of 30/1 to 500/1, a NiO/SiO₂ molar ratio of 0.001/1 to 0.01/1 or a NiO/SiO₂ molar ratio of 0.02/1, a surface area of 500 m²/g to 1,000 m²/g, an average pore diameter of about 1 nm (10 Å) (Angstroms) and a porosity of 0.3 ml/g to 0.6 ml/g, which is free of pores having a diameter greater than 3 nm (30 Å).

In the preferred embodiment, the silica/alumina/nickel oxide gel according to the invention has a SiO₂/Al₂O₃ molar ratio of 100/1, a NiO/SiO₂ molar ratio of 0.02/1, a surface area of 800 m²/g and a porosity of 0.4 to 0.5 ml/g.

In another aspect, the present invention relates to a process for producing the silica/alumina/nickel oxide gel according to claim 1 or claim 2, comprising the steps of:

(i) preparing an aqueous solution of a water-soluble aluminium compound which can be hydrolysed to Al₂O₃ and a tetraalkylammonium hydroxide, wherein the alkyl is selected from ethyl, n-propyl and n-butyl,

(ii) preparing an aqueous solution of a water-soluble nickel carboxylate and a water-soluble organic amine,

(iii) mixing the two solutions (i) and (ii) and adding a water-soluble silicon compound that can be hydrolyzed to SiO₂ to obtain a homogeneous gel, and

(iv) Drying the gel and calcining it first in an inert atmosphere and finally in an oxidising atmosphere.

The aluminum compounds used are preferably aluminum trialkoxides, i.e. aluminum tri-n-propoxide and aluminum tri-isopropoxide.

The nickel carboxylate is preferably a nickel salt of an aliphatic carboxylic acid and in particular nickel acetate. Silicon compounds are preferably the tetraalkyl silicates such as tetraethyl silicate. These reactants should advantageously be used in such ratios to obtain the composition desired for the silica/alumina/nickel oxide gel, taking into account that the reaction yield is almost quantitative.

The organic amine is preferably an aliphatic amine, especially ethylenediamine. Conveniently, an amount of amine is used to give a molar ratio of amine to nickel carboxylate of about 2/1.

The preparation of the solutions and their mixtures is advantageously carried out at room temperature or at a temperature close to room temperature. The hydrolysis of step (iii) is carried out at a temperature of 50 to 70°C and preferably 60°C. Under such conditions, the time required for complete gel formation varies from 15 minutes to 5 hours as a function of the preselected temperature and is, in a preferred embodiment, 25 to 60 minutes.

The drying step (iv) is conveniently carried out at a temperature below 150°C, preferably from 90 to 100°C, for a time sufficient to completely remove water. The calcination step (iv) is carried out in an atmosphere which is initially inert (such as nitrogen) and then oxidising (such as air), at a temperature of from 500 to 700°C, preferably from 550 to 600°C, for times ranging from 4 hours to 20 h, as a function of the preselected temperature and which in the preferred embodiment is 6 to 16 h.

The silica/alumina/nickel oxide gel thus obtained can be granulated into particles of the desired size or it can be supported by an appropriate inert solid substrate material or it can be mixed with an inert solid material. In particular, the gel can be mixed with appropriate metal oxides which essentially serve as binders. Oxides suitable for this purpose are aluminas, silicas and the oxides of titanium, magnesium and zirconium. The gel and the binder can be mixed in weight ratios of from 50:50 to 95:5, preferably from 30:90 to 90:10. The two components can be mixed by conventional means and the mixture is conveniently compacted into the desired final form, such as in the form of extrudates and granules. This makes it possible to impart improved mechanical properties to the catalyst.

According to a further embodiment, the present invention relates to an olefin oligomerization process using as catalyst the above-mentioned silica/alumina/nickel oxide gel.

For the purposes of the invention, oligomerization is understood to mean the conversion of isobutene to mixtures consisting essentially of α- and β-dimers as diisobutene, and oligomerization is understood to mean the conversion of propylene to mixtures consisting essentially of propylene dimers and trimers.

The oligomerization reaction can be carried out as a continuous or semi-continuous process or as a batch process operating in liquid, gaseous or mixed form (liquid/vapor). When operating discontinuously, the amount of catalyst advantageously employed is from 1 to 50% based on the olefin, at a temperature of from 50 to 150°C, preferably from 55 to 80°C, under a pressure of from 1.01325 bar (1 ata) to 202.65 bar (200 ata), preferably from 1.01325 bar (1 ata) to 6.195 bar (6 ata).

When operating semi-continuously or continuously, it is convenient to operate at a temperature of 50 to 2000, preferably 50 to 1500, with an olefin space velocity (WHSV) of 0.5 h⁻¹ to 8 h⁻¹. In any case, it is possible to use pure olefins or olefins mixed with other olefins and/or paraffins. The oligomerization reaction is exothermic, so the reactor temperature should be checked to avoid an excessively high Temperature increase leads to the formation of higher oligomers and/or undesirable isomerization phenomena.

As stated above, the olefins to be oligomerized according to the present invention are isobutene and propylene. In particular, the oligomerization of isobutene proceeds selectively to form the two isomers 2,4,4-trimethyl-1-pentene (α-diisobutene) and 2,4,4-trimethyl-2-pentene (β-diisobutene).

These dimers can be used as chemical intermediates for the preparation of non-ionic surfactants, crosslinking agents for elastomers, plasticizers and other chemicals, through alkylation, amination or carbonylation reactions.

In addition, α- and β-diisobutene are suitable in the production of high octane gasolines because they show the following ROM and MON values (unleaded): RON 106 and MON = 86.5 (α-isomer) and RON = 103.5 and MON = 86.2 (β-isomer) and can be hydrogenated to isooctane (2,2,4-trimethylpentane) with ROM = 100 and MON = 100.

When propylene is oligomerized, an oligomer mixture is obtained which mainly contains a high octane gasoline fraction (boiling point of C5 at 175ºC) together with a small amount of a higher molecular weight hydrocarbon fraction (boiling point of 175 to 370ºC).

The following test examples are given to better explain the invention.

example 1 Production of the catalyst (A) Solution

2 g of aluminum isopropylate are dissolved at room temperature in 68.5 g of a 13.35 wt.% aqueous solution of tetrapropylammonium hydroxide (TPA-OH).

(B) Solution

1.85 g of nickel acetate are dissolved in 75.6 (g) of demineralized water and 1.25 g of ethylenediamine (EDA) are added.

Solutions (A) and (B) are combined and the mixture is heated to 600: 104.1 g of tetraethyl silicate (TES) are added to the heated mixture.

The resulting mixture has the following molar ratios:

SiO₂/Al₂O₃ = 102

TPA-OH/SiO2 = 0.09

NiO/SiO₂ = 0.021

EDA/NiO = 2

This mixture is kept at 60°C for 40 minutes with stirring until a homogeneous gel is obtained, which is dried in a stream of air at 90°C and then calcined at 550°C, first for 3 hours under a stream of nitrogen and then for 10 hours under a stream of air.

A silica/alumina/nickel oxide gel is obtained in quantitative yield based on the original materials used, and this gel is granulated into 1 to 2 mm particles.

The catalyst produced in this way has the following specifications:

- X-ray amorphous (powder analysis with a Philips vertical goniometer, using Cuka radiation).

- SiO₂/Al₂O₃ molar ratio = 102

- NiO/SiO₂ molar ratio = 0.021

- Surface area = 800 m²/g (measured according to the B.E.T method in a Sorptomatic 1880 device by Carlo Erba);

- Porosity = 0.44 ml/g (average diameter 1 nm (10 Angstroms) and absence of pores with a diameter greater than 3 nm (30 Angstroms): (values determined using the Sorptomatik 1880 device by Carlo Erba).

Example 2

A glass vial, sealed under a nitrogen atmosphere and containing 2.13 g of the catalyst prepared according to Example 1, finely ground in a mortar and heated to 550°C for 6 hours, is placed in a 200 ml autoclave. The autoclave is evacuated, filled with nitrogen to a pressure of 1.01325 bar (1 ata) and 9.4 g of isobutene are condensed in it in the cold. The isobutene dimerization reaction is started by breaking the vial containing the catalyst with the mechanical stirrer with which the autoclave is equipped. Dimerization is a strongly exothermic reaction and the actual reaction temperature is monitored with a thermocouple inserted inside the autoclave. By varying the temperature of the bath it is possible to monitor the temperature fluctuations within ± 2°C. During the entire reaction, the pressure inside the autoclave is essentially the vapor pressure of unreacted isobutene. Consequently, While the initial pressure is about 6.195 bar (6 ata), corresponding to the vapor pressure of the isobutene in equilibrium with its liquid phase, the pressure decreases as dimerization progresses, due to the disappearance of the liquid isobutene phase, followed by a gradual disappearance of the vapor phase concerned.

Samples of the reaction mixture are taken from the autoclave at different times using a dip tube and the samples are condensed into test tubes equipped with a set-up for subsequent analysis. Vigorous mechanical stirring is maintained throughout the course of the reaction to ensure both adequate contact between the liquid and the solid (catalyst) and good homogeneity of the mixture during sampling.

The conversion and quantitative analysis of the mixed products, corresponding to the different samples, is carried out by gas chromatography using a Hewlett Packard large-orifice chromatography column containing an RSL300 nonpolar stationary phase, programmed at a temperature of 30 to 280ºC.

The quantitative determination of the various isomers of the isobutene dimer, i.e. 2,4,4-trimethyl-1-pentene (α-diisobutene) and 2,4,4-trimethyl-2-pentene (β-diisobutene) is again carried out by gas chromatography using a capillary column with a stationary apolar phase, SPB1, which allows the separation of the isomers, while their structural identification is carried out on a mixture containing 96% of the dimer and obtained by fractional distillation of the first sample taken during the reaction, using a mass spectrometer fitted to the capillary column gas chromatograph, based on ¹H and ¹³C NMR.

The results are summarized in Table 1.

Example 3

The procedure is similar to that of Example 2, with the same catalyst as in Example 2, which has been reactivated by heating at 550°C for 6 hours, the reaction temperature being the same as in Example 2, but with half the amount of catalyst by weight as in Example 2. Specifically, 2 g of activated catalyst and 18 g of isobutene are introduced into the autoclave.

In this case, the starting temperature is 55ºC, so that the heat contributed by the dimerization reaction results in an increase to about 60ºC of the internal temperature of the autoclave (oil bath temperature) during the first 60 s, while the reaction temperature stabilizes well.

The results of this experiment are summarized in Table 1. Table 1 Example Temperature, ºC Catalyst, wt.% Isobutene conversion, % after min Oligomer composition, % C16 and higher Table 1 (continued) Example Dimer composition after min Other traces

Example 4

3.0 g (5 ml) of the catalyst prepared according to Example 1 are placed in a steel flow reactor with an internal diameter of 12 mm, which is heated with an electric furnace. Propylene is introduced into the reactor under the following operating conditions:

- Inlet temperature 80ºC

- Hot spot temperature 94ºC

- Pressure 30.8 bar (30 ata)

- Space velocity 2.87 h⊃min;¹

Under the conditions given above, the following results are obtained:

- Propylene conversion 79%

- Witches 45%

- Nonene 40 %

- Oligomers over 09 15 %

The portion of the product containing hydrocarbons with up to 9 carbon atoms is a high-grade gasoline with the following values ROM = 97 and MON = 84 (unleaded).

Example 5

Propylene is introduced into the flow reactor of Example 4, which is charged with the same catalyst and the same amounts of reactants, under the following operating conditions:

- Inlet temperature 120ºC

- Hot spot temperature 135ºC

- Pressure 30.8 bar (30 ata)

- Space velocity 4.59 h⊃min;¹

Under the conditions given above, the following results are achieved:

- Propylene conversion 73%

- Witches 25%

- Nonene 35%

- Oligomers higher than 09 40 %

The portion of the product containing hydrocarbons with up to 9 carbon atoms is a high-grade gasoline with the following values ROM = 97 and MON = 84 (unleaded).

Claims (13)

1. X-ray amorphous silica/alumina nickel oxide gel with: a molar ratio SiO₂/Al₂O₃ of 30:1 to 500:1, a molar ratio NiO/SiO₂ of 0.001:1 to 0.01:1, or a molar ratio NiO/SiO₂ of 0.02:1, a surface area of 500 m²/g to 1000 m²/g, a porosity of 0.3 ml/g to 0.6 ml/g, with an average pore diameter of 1 nm (10 Å), and which is free of pores with a diameter of more than 3 nm (30 Å). 2. Silica/alumina/nickel oxide gel according to claim 1, wherein the molar ratio SiO₂/Al₂O₃ is 100:1, the molar ratio NiO/SiO₂ is 0.02:1, the surface area is 800 m²/g and the porosity is 0.4 to 0.5 ml/g. 3. Silica/alumina/nickel oxide gel according to claim 1 or 2, wherein the gel is either on an inert solid substrate or in admixture with an inert solid material. 4. A process for producing the silica/alumina/nickel oxide gel according to claim 1 or claim 2, comprising the steps of: (i) preparing an aqueous solution of a water-soluble aluminium compound which can be hydrolysed to Al₂O₃ and a tetraalkylammonium hydroxide, wherein the alkyl is selected from ethyl, n-propyl and n-butyl, (ii) preparing an aqueous solution of a water-soluble nickel carboxylate and a water-soluble organic amine, (iii) mixing the two solutions (i) and (ii) and adding a water-soluble silicon compound which can be hydrolysed to SiO₂ to obtain a homogeneous gel, and (iv) Drying the gel and calcining it first in an inert atmosphere and finally in an oxidizing atmosphere. 5. Process according to claim 4, wherein in step (i) the aluminum trialkoxides and preferably aluminum tri-n-propoxide and aluminum tri-isopropoxide are used as aluminum compounds. 6. Process according to claim 4, wherein in step (ii) the nickel carboxylates used are the nickel salts of an aliphatic carboxylic acid and preferably nickel acetate, and the organic amines used are the aliphatic diamines and preferably ethylenediamine, with a molar ratio of amine to nickel carboxylate of 2:1. 7. Process according to claim 4, wherein in step (ii) the silicon compounds used are the tetraalkyl silicates, and preferably tetraethyl silicate. 8. Process according to claim 4, wherein the hydrolysis of step (iii) is carried out at a temperature of 50°C to 70°C, and preferably at 60°C, for a period of from 15 minutes to 5 hours, and preferably from 25 minutes to 60 minutes. 9. Process according to claim 4, wherein the drying step (iv) is carried out at a temperature below 150°C, and preferably from 90°C to 100°C, for a time sufficient to completely remove the water, the calcination is carried out in an atmosphere which is initially inert, and is preferably nitrogen, and then in an oxidizing atmosphere, preferably in air, at a temperature of from 500°C to 700°C, preferably from 550°C to 600°C, for a time of from 4 hours to 20 hours, and preferably from 6 hours to 16 hours. 10. A process for dimerizing isobutene to α- and β-isobutene comprising the step of contacting isobutene under dimerization conditions with the silica/alumina/nickel oxide gel of claims 1, 2 and 3. 11. A process for preparing propylene dimers and trimers comprising the step of contacting propylene under oligomerization conditions with the silica/alumina/nickel oxide gel of claims 1, 2 and 3. 12. A process according to claim 10 or claim 11, wherein the process is carried out as a batch process, with a catalyst amount of from 1 to 50% by weight based on the olefin, at a temperature of from 50°C to 150°C, preferably from 55°C to 80°C, under a pressure of from 1.01325 bar (1 ata) to 202.65 bar (200 ata), and preferably from 1.01325 bar (1 ata) to 6.185 bar (6 ata). 13. A process according to claim 10 or claim 11, wherein the process is carried out as a semi-continuous process or as a continuous process at a temperature of 50°C to 200°C, preferably from 50°C to 150°C, with an olefin space velocity (WHSV) of 0.5 h⁻¹ to 8 h⁻¹.